Control valves of this kind are generally known. For instance, mushroom-type valves which can be actuated from outside by drives are used to control the fluid flow in lines of an internal combustion engine. Mushroom valves consist of a valve stem and axial adjacent valve plate, usually made of solid material. For example, the valves are mounted in lines through which fluid flows and fluid can flow around them. Moreover, spring means can be associated with the valves to assist the drives.
It should be noted, however, that the forces for the actuation of the valves vary because of different levels of pressure, in a cooling system, for example. Furthermore, sealing the adjusting mechanism against aggressive fluids containing impurities causes additional problems.